#include <stdio.h>
#include <string.h>
void build_index_url(const char *domain, char *index_url);
int main(void)
{
    char url[50];
    build_index_url("knking.com", url);
    puts(url);
    return 0;
}
void build_index_url(const char *domain, char *index_url) {
    strcpy(index_url, "http://www.");
    strcat(index_url, domain);
    strcat(index_url, "/index.html");
}